Hovelacque (1967) was the first to propose the subdivision of jugular foramen. The foramen is divided by a fibrous or bony septum that joins the jugular spine of the petrous bone to the jugular process of occipital bone, the anteromedial compartment (pars nervosa) and a posterolateral compartment (pars vascularis).

Katsuta el al., divided the jugular foramen into three compartments: two venous and a neural or intrajugular compartment. The venous compartments consist of a larger posterolateral venous channel, the sigmoid part, which receives the flow of the sigmoid sinus, and a smaller anteromedial venous channel, the petrosal part, which receives the drainage of the inferior petrosal sinus. The petrosal part forms a characteristic venous confluens by also receiving tributaries from the hypoglossal canal, petroclival fissure, and vertebral venous plexus. The petrosal part empties into the sigmoid part through an opening in the medial wall of the jugular bulb between the glossopharyngeal nerve anteriorly and the vagus and accessory nerves posteriorly. The intrajugular or neural part, through which the glossopharyngeal, vagus, and accessory nerves course, is located between the sigmoid and petrosal parts at the site of the intrajugular processes of the temporal and occipital bones, which are joined by a fibrous or osseous bridge. The glossopharyngeal, vagus, and accessory nerves penetrate the dura on the medial margin of the intrajugular process of the temporal bone to reach the medial wall of the internal jugular vein. The operative approaches, which access the foramen and adjacent areas and are demonstrated in a stepwise manner, are the postauricular transtemporal, retrosigmoid, extreme lateral transcondylar, and preauricular subtemporal-infratemporal approaches
6).

Clinical significance

Damage to the motor division of the lower cranial nerves that run into the jugular foramen leads to hoarseness, dysphagia, and the risk of aspiration pneumonia; therefore, its functional preservation during surgical procedures is important. Intraoperative mapping and monitoring of the motor rootlets at the cerebellomedullary cistern using endotracheal tube electrodes is a safe and effective procedure to prevent its injury.

Approaches

Tumors involving the jugular foramen (JF) have a variable relationship to the neurovascular structures (jugular vein, cranial nerves IX-XI) that traverse this conduit through the skull base. The surgeon familiar with the site of origin, growth pattern, and geometry of each of the common lesions affecting this region with respect to surrounding nerves and vessels is at a considerable advantage when undertaking a function-sparing procedure.

The endoscopic transnasal/transmaxillary transpterygoid corridor provides a less invasive route for selected lesions in the jugular foramen than the traditional open route through the preauricular subtemporal infratemporal fossa approach. However, the anterior endoscopic approach provides a smaller channel to the jugular foramen than the preauricular approach.

The anterior endoscopic approach to the anterolateral part of the jugular foramen is a useful alternative to the lateral microsurgical preauricular approach in carefully selected cases. The vaginal process of the tympanic part of the temporal bone provides a valuable landmark to aid in accessing the jugular foramen in both procedures and can be drilled to open the foramen in the preauricular approach
8).

Cohen et al., describe the rectus capitis lateralis (RCL) and its anatomical relationships, and discuss its utility as a surgical landmark for safe exposure of the jugular foramen in extended or combined skull base approaches. In addition, the condylar triangle is defined as a landmark for localizing the vertebral artery (VA) and occipital condyle.

Four cadaveric heads (8 sides) were used to perform far-lateral, extended far-lateral, combined transmastoid infralabyrinthine transcervical, and combined far-lateral transmastoid infralabyrinthine transcervical approaches to the jugular foramen. On each side, the RCL was dissected, and its musculoskeletal, vascular, and neural relationships were examined.

The RCL lies directly posterior to the internal jugular vein-only separated by the carotid sheath and in some cases cranial nerve (CN) XI. The occipital artery travels between the RCL and the posterior belly of the digastric muscle, and the VA passes medially to the RCL as it exits the C-1 foramen transversarium and courses posteriorly toward its dural entrance. CNs IX-XI exit the jugular foramen directly anterior to the RCL. To provide a landmark for identification of the occipital condyle and the extradural VA without exposure of the suboccipital triangle, Cohen et al., propose and define a condylar triangle that is formed by the RCL anteriorly, the superior oblique posteriorly, and the occipital bone superiorly.

The RCL is an important surgical landmark that allows for early identification of the critical neurovascular structures when approaching the jugular foramen, especially in the presence of anatomically displacing tumors. The condylar triangle is a novel and useful landmark for identifying the terminal segment of the hypoglossal canal as well as the superior aspect of the VA at its exit from the C-1 foramen transversarium, without performing a far-lateral exposure
9).